In telecommunication or other systems using electromagnetic radiation signal beams, it is often desirable to switch a beam of electromagnetic radiation arriving at an input optical port selectively into either one of a pair of output ports--for example, to switch an optical signal beam arriving at the output end of an input optical fiber selectively into either one of a pair of exit opticals fibers depending upon a switching control signal at any moment of time. More specifically, in a telecommunication switching system, it is often desired to reroute an optical communication path--that is, to switch an optical path (IA), running from a given input fiber (I) to a first output optical fiber (A), into a second path (IB), running from the input fiber (I) to a second output optical fiber (B), and to switch the second path (IB) back into the first path (IA).
For another example, a local area network (LAN) typically includes a main computer station (M) and an optical fiber LAN loop (ring) composed of fiber segments arranged in a loop, together with local stations (X,Y,Z. . .) located at the junctions of successive fiber segments. Each of the local stations typically comprises a separate local personal computer or the like. Optical switching arrangements are required to bypass local stations that are defective or to bypass all local stations in cases where a defect in the loop itself occurs.
Prior art is exemplified by the optical switching arrangement described in a paper by M. Nunoshita et al, published in Optics Letters, vol. 4, No. 1, pp. 27-28 (1979). In that paper, optical switches for the above-described purposes employed a moving lens to switch the optical paths. But such switches are very clumsy and costly, primarily because of the need to move relatively heavy piece parts rather quickly. Moreover, the conventional machine-made parts required for these switches lack sufficient precision of optical alignment to be used in conjunction with optical fibers unless undesirably costly and time-consuming alignment procedures for each switch are performed. Furthermore, long-term stability and reliability are problematical because of aging phenomena associated with parts having differing mechanical and thermal properties. In addition, these switches do not enable temporarily non-accessed (off-line) local stations in a LAN to perform desired self-testing operations in conjunction with the local optical source, unless extra added complexity is introduced: for example, an the added complexity of extra fiber, which can be added as described in Electro-Optic Products, Application Note 102, FIG. 4 therein, published by Siecor Corp., Research Triangle Park, N. C. 27709. Furthermore, in the switches described in that Siecor publication, mechanical stops are required, which tend to wear out in use and which cause the optical components to vibrate immediately after switchings in such a direction as to jitter the beam undesirably.
It would therefore be desirable to have an optical signal switching arrangement, and more generally an electromagnetic signal switching arrangement, which mitigates the above shortcomings in the prior art.